Even low levels of heavy metals (for example arsenic, lead, cadmium, mercury, etc.) in drinking water are considered detrimental to a person's health, and in the case of infants, are believed to impede intellectual development. For example, in babies and children, exposure to lead in drinking water above the action level can result in delays in physical and mental development, along with slight deficits in attention span and learning abilities. In adults, lead exposure via drinking water can cause increases in blood pressure, as well as the development of kidney problems.
Recognizing these hazards, the Environmental Protection Agency (EPA) has established limits on the presence of heavy metals in drinking water. For example, no more than 15 parts per billion (15 ppb) of lead may be present in public water systems. In addition, industrial water streams must contain less than 0.5 ppm of heavy metals before the water can be discharged.
In addition to reducing the heavy metals to acceptable EPA levels, it is desirable to improve the taste, odor and smell of drinking water by removing chlorine, ionic metals, organic molecules and colloidal particles. Ion exchangers, both organic and inorganic, including crystalline molecular sieve zeolites, are known to remove certain metals from aqueous systems such as drinking water. Activated carbon is also used in water purification or remediation processes. Activated carbon improves taste, odor and smell by adsorbing ionic metals, organic molecules and colloidal particles and also removes chlorine.
In addition to esthetic effects, elevated levels of certain contaminants, for example halogenated organic compounds, are known to be able to detrimentally impact health in ways such as increasing the risk of certain cancers.
The purification of drinking water is often accomplished at its point of use, such as under-the-counter, on-the-counter, whole house systems, end-of-tap, or free standing gravity flow carafe type devices. For industrial/commercial applications, packed bed systems are typically used.
There is an ongoing effort to develop improved products which meet or exceed EPA and other regulatory body requirements for heavy metals and halogenated byproducts removal as well as improved taste, color and odor, and have flow rates which are commercially acceptable. In circumstances where the filter size is limited and/or high flow rates are required, there is particular need for effective drinking water purification techniques.